Severe hemorrhage is the leading cause of death among trauma victims, and is responsible for approximately 3 million deaths worldwide. Much of the mortality may be prevented by the timely availability of a safe and uni- versal resuscitation fluid. While whole blood or red blood cells (RBCs) remain the preferred transfusion fluids, inadequate availability of safe blood remains a problem. Despite the optimism in combating transfusion-related infections and ensuring an educated donor population, the limited shelf-life of blood and the need to cross- match frequently cause blood inventory shortages. These issues have stimulated a search for safe, immune- tolerant, shelf-stable and efficacious oxygen carrier for both civilian emergency and military applications. He- moglobin based oxygen carriers increase both oxygen-carriage and cardiac preload. We are developing liposome-encapsulated hemoglobin or LEH as a substitute oxygen carrier closely mimick- ing the RBCs. Encapsulated hemoglobin is believed to have better control over hemodynamics as compared to other chemically-modified, but free hemoglobin products. Using a novel formulation and advanced processing technologies, we have overcome the barriers of low encapsulation, oxidative instability, expense and scale-up. The product (called NeoLEH) circulates in blood for a prolonged time, and improves cerebral metabolism. Pre- liminary data demonstrate that the smaller size of LEH (275 nm) as compared to the RBCs (7.5 5m) results in more efficient oxygen delivery to the brain, which in turn improves cerebral oxygen and energy metabolism. In the proposed work, we will test our overall hypothesis that NeoLEH improves survival and cerebral metabol- ism, and serves as a long-circulating and non-toxic oxygen carrier in hemorrhagic shock. The specific aims are to assess: 1) Survival and cerebral metabolism in a rat model of 40% hemorrhage, 2) Pharmacokinetics and biodistribution of NeoLEH, and the effect of reinjection, 3) Acute toxic effects of NeoLEH in the animal model of 40% hemorrhage, and 4) NeoLEH resuscitation and ischemia-reperfusion (I/R) injury. We propose a 4-y project for testing efficacy and safety of NeoLEH. We will study 24 h survival of rats receiv- ing NeoLEH resuscitation after 40% blood loss. Ringer's lactate, shed blood and Hextend will be used as con- trol fluids. Improvement in cerebral oxygen, glucose and energy metabolism will be evaluated by positron emission tomography and magnetic resonance imaging. Circulation persistence and biodistribution of NeoLEH will be assessed by monitoring the blood and organ levels of radiolabeled 99mTc-NeoLEH. In order to test the safety of NeoLEH, acute effects of NeoLEH infusion on phagocytic capacity of liver and complement-mediated platelet activation will be studied. Lastly, we will assess if NeoLEH infusion has any salutary effects in ische- mia-reperfusion phenomenon by monitoring intestinal integrity, neutrophil sequestration, etc. The results of the proposed investigations will be critical for the clinical development of NeoLEH. Targeted towards resuscitation in acute blood loss due to surgery or trauma, NeoLEH will serve civilian as well as military needs alike.